var canvas = document.getElementById("cas");
var ctx = canvas.getContext("2d");
resize();
window.onresize = resize;

function resize() {
	canvas.width = window.innerWidth || document.documentElement.clientWidth || document.body.clientWidth;
	canvas.height = window.innerHeight || document.documentElement.clientHeight || document.body.clientHeight;
}
var RAF = (function() {
	return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || window.oRequestAnimationFrame || window.msRequestAnimationFrame || function(callback) {
		window.setTimeout(callback, 1000 / 60);
	};
})();
// 鼠标活动时，获取鼠标坐标
var warea = { x: null, y: null, max: 20000 };
window.onmousemove = function(e) {
	e = e || window.event;
	warea.x = e.clientX;
	warea.y = e.clientY;
};
window.onmouseout = function(e) {
	warea.x = null;
	warea.y = null;
};
// 添加粒子
// x，y为粒子坐标，xa, ya为粒子xy轴加速度，max为连线的最大距离
var dots = [];
for(var i = 0; i < 150; i++) {
	var x = Math.random() * canvas.width;
	var y = Math.random() * canvas.height;
	var xa = Math.random() * 2 - 1;
	var ya = Math.random() * 2 - 1;
	dots.push({
		x: x,
		y: y,
		xa: xa,
		ya: ya,
		max: 6000
	})
}
// 延迟100秒开始执行动画，如果立即执行有时位置计算会出错
setTimeout(function() {
	animate();
}, 10);
// 每一帧循环的逻辑
function animate() {
	ctx.clearRect(0, 0, canvas.width, canvas.height);
	// 将鼠标坐标添加进去，产生一个用于比对距离的点数组
	var ndots = [warea].concat(dots);
	dots.forEach(function(dot) {
		// 粒子位移
		dot.x += dot.xa;
		dot.y += dot.ya;
		// 遇到边界将加速度反向
		dot.xa *= (dot.x > canvas.width || dot.x < 0) ? -1 : 1;
		dot.ya *= (dot.y > canvas.height || dot.y < 0) ? -1 : 1;
		// 绘制点
		ctx.fillRect(dot.x - 0.5, dot.y - 0.5, 1, 1);
		// 循环比对粒子间的距离
		for(var i = 0; i < ndots.length; i++) {
			var d2 = ndots[i];
			if(dot === d2 || d2.x === null || d2.y === null) continue;
			var xc = dot.x - d2.x;
			var yc = dot.y - d2.y;
			// 两个粒子之间的距离
			var dis = xc * xc + yc * yc;
			// 距离比
			var ratio;
			// 如果两个粒子之间的距离小于粒子对象的max值，则在两个粒子间画线
			if(dis < d2.max) {
				// 如果是鼠标，则让粒子向鼠标的位置移动
				if(d2 === warea && dis > (d2.max / 2)) {
					dot.x -= xc * 0.01;
					dot.y -= yc * 0.01;
				}
				// 计算距离比
				ratio = (d2.max - dis) / d2.max;
				// 画线
				ctx.beginPath();
				ctx.lineWidth = ratio / 2;
				ctx.strokeStyle = 'rgba(30,144,255,' + (ratio + 0.2) + ')';
				ctx.moveTo(dot.x, dot.y);
				ctx.lineTo(d2.x, d2.y);
				ctx.stroke();
			}
		}
		// 将已经计算过的粒子从数组中删除
		ndots.splice(ndots.indexOf(dot), 1);
	});
	RAF(animate);
}